multi: add NewLogClosure in lnutils to avoid repetition

And replaces all usage of `logClosure` with `lnutils.LogClosure`.

rpcserver.go

@@ -63,6 +63,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/walletrpc"
 	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnutils"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/btcwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
@@ -5845,7 +5846,7 @@ func (r *rpcServer) LookupInvoice(ctx context.Context,
 	}
 
 	rpcsLog.Tracef("[lookupinvoice] located invoice %v",
-		newLogClosure(func() string {
+		lnutils.NewLogClosure(func() string {
 			return spew.Sdump(invoice)
 		}))